Compliant foil fluid film radial bearing

ABSTRACT

A multi-segment radial bearing including a bushing with an interior bore having a plurality of anti-rotation retainers which are equally spaced and extend the axial length of the interior bore. The generally T-shaped retainers divide the interior bore of the bushing into a like plurality of lobes, with each lobe having a compliant foil and a foil underspring disposed between adjacent generally T-shaped retainers.

TECHNICAL FIELD

This invention relates to the general field of compliant foil fluid filmbearings and more particularly to an improved multi segment compliantfoil fluid film radial bearing.

BACKGROUND OF THE INVENTION

Compliant foil fluid film radial bearings are currently being utilizedin a variety of high speed rotor applications. These bearings aregenerally comprised of a bushing, a rotating element such as a rotor orshaft adapted to rotate within the bushing, non-rotating compliant fluidfoil members mounted within the bushing and enclosing the rotatingelement, and non-rotating compliant spring foil members mounted withinthe bushing underneath the non-rotating compliant fluid foil members.The space between the rotating element and the bushing is filled withfluid (usually air) which envelops the foils. Conventionally, thecompliant fluid foil elements are divided into a plurality of individualcompliant foils to form a plurality of wedge shaped channels whichconverge in thickness in the direction of the rotation of the rotor.

The motion of the rotating element applies viscous drag forces to thefluid in the converging wedge channels. This results in increases influid pressure, especially near the trailing end of the wedge channels.If the rotating element moves toward the non-rotating element, theconvergence angle of the wedge channel increases, causing the fluidpressure rise along the channel to increase. Conversely, if the rotatingelement moves away, the pressure rise along the wedge channel decreases.Thus, the fluid in the wedge channels exerts restoring forces on therotating element that vary with and stabilize running clearances andprevent contact between the rotating and non-rotating elements of thebearing. Flexing and sliding of the foils causes coulomb damping of anyaxial or overturning motion of the rotating element of the bearing.

Owing to preload spring forces or gravity forces, the rotating elementof the bearing is typically in physical contact with the fluid foilmembers of the bearing at low rotational speeds. This physical contactresults in bearing wear. It is only when the rotor speed is above whatis termed the lift-off/touch-down speed that the fluid dynamic forcesgenerated in the wedge channels assure a running gap between therotating and non-rotating elements.

Compliant foil fluid film radial bearings typically rely on backingsprings to preload the fluid foils against the relatively movablerotating element so as to control foil position/nesting and to establishfoil dynamic stability. The bearing starting torque (which shouldideally be zero) is directly proportional to these preload forces. Thesepreload forces also significantly increase the rotor speed at which thehydrodynamic effects in the wedge channels are strong enough to lift therotating element of the bearing out of physical contact with thenon-rotating members of the bearing. These preload forces and the highlift-off/touchdown speeds result in significant bearing wear each timethe rotor is started or stopped.

Conventional compliant foil fluid film radial bearings operate withextremely small running clearances and moderate, as opposed to low, dragand power consumption. The clearances between the non-rotating fluidfoil's converging channel ramp trailing ends and the rotating elementare typically less than 100 micro-inches at operating conditions.

While most prior compliant foil fluid film radial bearings utilize aplurality of individual compliant foils and individual spring foils witha cylindrically bored bushing, there are instances where a singlecompliant foil and a single spring foil have been proposed with a camshaped or lobed bushing. An example of this type of radial bearing canbe found in U.S. Pat. No. 5,427,455 issued Jun. 27, 1995 to Robert W.Bosley, entitled “Compliant Foil Hydrodynamic Fluid Film RadialBearing”.

SUMMARY OF THE INVENTION

The present invention is directed to a multi-segment radial bearinggenerally comprising a bushing, a shaft or rotor, a plurality ofcompliant foils, and a like plurality of foil undersprings.

The interior bore of the bushing includes a plurality of anti-rotationretainers that are equally spaced and extend the axial length of theinterior bore, which may be either cylindrical or contoured. Thesegenerally T-shaped retainers divide the interior bore of the bushinginto a like plurality of lobes, with each lobe having a compliant foiland foil underspring disposed therein between adjacent generallyT-shaped retainers.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the present invention in general terms, referencewill now be made to the accompanying drawings in which:

FIG. 1 is an end view of the compliant foil fluid film radial bearing ofthe present invention;

FIG. 2 is an enlarged sectional view of a portion of the compliant foilfluid film radial bearing of FIG. 1;

FIG. 3 is an exploded perspective view of the compliant foil fluidradial bearing of FIGS. 1 and 2; and

FIG. 4 is an enlarged sectional view of a portion of an alternatecompliant foil fluid film radial bearing of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrated in FIGS. 1-3 is the compliant foil fluid film radial bearing10 of the present invention. This multi-segment radial bearing 10generally comprises a bushing 12, a shaft or rotor 14, a plurality ofcompliant foils 16 (shown as three), and a like plurality of foilundersprings 18.

The interior bore 20 of the bushing 12 includes a plurality ofanti-rotation devices or retainers 22 (shown as three, generallyT-shaped retainers) which are equally spaced and extend the axial lengthof the interior bore 20. The retainers 22 divide the interior bore 20 ofthe bushing 12 into a like plurality of lobes 24. The compliant foils 16and the foil undersprings 18 are disposed in each lobe 24 betweenadjacent generally T-shaped retainers 22.

While the shaft or rotor 14 is cylindrical, the interior bore 20 of thebushing 12 may or may not be cylindrical. If the interior bore 20 is notcylindrical, the generally T-shaped retainers 22 will divide theinterior bore 20 into a plurality of shaped or contoured lobes 24.

On the other hand, if the interior bore 20′ of the bushing 12′ iscylindrical, the generally T-shaped retainers will divide the interiorbore 20′ into a plurality of equally spaced arc segments of a cylinderand the converging wedges will be formed via the compliant foil 16′and/or the foil undersprings 18′ as generally shown in FIG. 4. Theheight of the foil undersprings 18′ may increase from the leading edgeof the compliant foil 16′ to the trailing edge of the compliant foil 16′in order to form the converging wedge. Alternately, the stiffness of thefoil underspring can vary from the leading edge to the trailing edge toproduce the same result, or shims of varying height can be positionedunderneath the foil underspring.

The generally T-shaped retainers 22 may be symmetrical or conform to theleading edge and trailing edge of the contoured lobes 24.Non-symmetrical T-shaped retainers 22 will retain the foils 16 atdifferent radii from the geometric center with the leading edge of thefoils retained at a greater geometric radius than the trailing edge.

The generally T-shaped retainers 22 are formed as part of the contouredinterior bore 20 of the bushing 12 with the base 26 thereof extendingradially inwards from the interior bore 20. The cross piece of thegenerally T-shaped retainers 22 has a leading edge 30 and a trailingedge 28, with the leading edge 30 having a greater thickness or widththan the trailing edge 28 as best shown in FIG. 2. Since the innerdiameter of the cross piece is the same at both the leading edge 30 andthe trailing edge 28, this provides a greater diameter or depth for thetrailing edge of the contoured lobe 24 which is under the thickerleading edge 30 of the generally T-shaped retainers 22.

The contoured surface of the lobes 24 can be derived from one or aseries of radii of a defined profile. For example, in the case of three(3) foil segments, the contour of the lobes 24 in which the compliantfoils 16 and underspring foils 18 rest upon can be a multiple of, or afraction of, a specific number. Also, an appropriate contour can beconstructed from vertices of an equilateral triangle of specific lengthside with circles formed from these vertices intersecting to give thecontoured surface which may be machined, ground, EDM'ed or broached.

While a preferred embodiment of the compliant foil fluid film radialbearing 10 is shown with three (3) compliant foil segments 16 and three(3) foil undersprings 18, a greater number of compliant foils segments16 and foil undersprings 18 can be utilized. For example, five (5) ormore segments may be equally appropriate for the compliant foil fluidfilm radial bearing 10.

The compliant foils 16 and foil undersprings 18 are trapped and heldbetween adjacent T-shaped retainers 22. The compliant foils 16 wouldnormally have a preformed arcuate shape as shown in FIG. 3. The foilundersprings 18 may have a preferred radius or simply be a rectangularsheet. In either case, the compliant foils 16 and foil undersprings 18are axially inserted, either separately or together, into the interiorbore 20 of bushing 12 between adjacent T-shaped retainers 22. Also,while the foil undersprings 18 are illustrated as a wavy springform, anyconventional bearing underspring can be utilized, including the springdescribed in U.S. Pat. No. 5,427,455. The underspring 18 may havevariable spring rates or tapered heights from the leading edge to thetrailing edge as shown in FIG. 4.

When trapped between adjacent T-shaped retainers 22, the compliant foils16 would be pre-loaded in compression between the adjacent T-shapedretainers 22. In some instances, however, the compliant foils 16 may bemerely retained in position between adjacent T-shaped retainers 22without preloading. The foil undersprings 18 would, however, normally bepre-loaded in compression between adjacent T-shaped retainers 22. Thefoil underspring 18 may contribute to the contoured shape of thecompliant foils 16. In most instances, the compliant foils 16 and foilunderspring 18 would be separate and would be capable of slidingmovement therebetween. There may, however, be instances where thecompliant foils 16 and foil underspring 18 will be joined together intoa single assembly.

The greater thickness of the leading edge 30 of the T-shaped retainercrosspiece produces a greater depth at the trailing edge of thecompliant foils 16 to serve as a means to pull the compliant foils 16away from the trailing edge of the converging wedge. The trailing edge28 of the T-shaped retainers 22 has less thickness thereby allowing theleading edge of the foils to rest closer to the shaft, which willfacilitate development of the fluid film wedges.

Also, while the compliant foil fluid film radial bearing 10 can functionhydrodynamically, by providing an external source of fluid underpressure, a hydrostatic aspect can be realized. The external pressurizedfluid may be introduced axially at the ends of the bushing or throughradial holes 40 in the bushing 40 axially along and through the T-shapedretainers 22. The hydrostatic aspect will provide cooling fluid to theinterior bore 20 of the bushing 12, which will increase bearing lifeespecially in a gas turbine application. Hydrostatic operation will alsoincrease the load capacity of the bearing.

The radial bearing 10 of the present invention allows for automation bymass production and the components can easily be assembled by hand. Thecompliant foils 16 may be stamped or fine blanked and there is norequirement for spot welding or chemical etching. The large clearancesbetween the compliant foils 16 and the shaft 14 at the T-shapedretainers 22 allow improved cooling of the shaft 14 and compliant foils16. The design can accommodate a variety of underspring types and theT-shaped retainers 22 permit more design flexibility with respect to theshaft, foil and spring interaction.

While specific embodiments of the invention have been illustrated anddescribed, it is to be understood that there are provided by way ofexample only and that the invention is not to be construed as beinglimited thereto but only by the proper scope of the following claims.

1. A compliant foil fluid film radial bearing comprising: a bushinghaving an interior bore including a plurality of equally spacedgenerally T-shaped retainers axially extending in said interior bore anda like plurality of lobes between adjacent generally T-shaped retainers;a shaft rotatably supported within said interior bore of said bushing; aplurality of compliant foils, with an individual compliant foil disposedin said interior bore of said bushing between adjacent generallyT-shaped retainers; and a plurality of foil undersprings, with anunderspring disposed beneath each of said compliant foils betweenadjacent generally T-shaped retainers.
 2. The compliant foil fluid filmradial bearing of claim 1 wherein said interior bore is cylindrical andsaid individual compliant foils and said individual foil underspringsbeneath said individual complaint foils establish a converging wedgebetween adjacent generally T-shaped retainers.
 3. The compliant foilfluid film radial bearing of claim 1 wherein said interior bore isnon-cylindrical, generally contoured lobes are formed between adjacentgenerally T-shaped retainers, and said individual compliant foils andsaid individual foil undersprings generally conform to the shape of saidcontoured lobes to establish a converging wedge.
 4. A compliant foilfluid film radial bearing comprising: a bushing having a cylindricalinterior bore including a plurality of equally spaced retainers axiallyextending into said interior bore and a like plurality of arc segmentsbetween adjacent retainers; a shaft rotatably supported within saidinterior bore of said bushing; a plurality of compliant foils, with anindividual compliant foil disposed in said interior bore of said bushingin each arc segment between adjacent retainers; and a plurality of foilundersprings, with an underspring disposed beneath each of saidcompliant foils in each arc segment between adjacent retainers, theradial height of said foil undersprings increasing form its leading edgeto its trailing edge to establish a converging wedge on the surface ofsaid compliant foil facing said shaft.
 5. The compliant foil fluid filmradial bearing of claim 4 wherein said retainers are generally T-shaped.6. The compliant foil fluid film radial bearing of claim 5 wherein saidgenerally T-shaped retainers are symmetrical.
 7. The compliant foilfluid film radial bearing of claim 5 wherein said generally T-shapedretainers are asymmetrical.
 8. The compliant foil fluid film radialbearing of claim 7 wherein said generally T-shaped asymmetricalretainers have a crosspiece with a leading edge and a trailing edge,with the leading edge thicker than the trailing edge.
 9. The compliantfoil fluid film radial bearing of claim 4 wherein the radial stiffnessof said foil undersprings increases form its leading edge to itstrailing edge.
 10. The compliant foil fluid film radial bearing of claim9 wherein said bearing is hydrodynamic.
 11. The compliant foil fluidfilm radial bearing of claim 9 wherein said retainers are generallyT-shaped.
 12. The compliant foil fluid film radial bearing of claim 9wherein said bearing is hydrostatic.
 13. A compliant foil fluid filmradial bearing comprising: a bushing having a non-cylindrical interiorbore including a plurality of equally spaced retainers axially extendinginto said interior bore and a like plurality of contoured lobes betweenadjacent retainers; a shaft rotatably supported within said interiorbore of said bushing; a plurality of compliant foils, with an individualcompliant foil disposed in said interior bore of said bushing in eachcontoured lobe between adjacent retainers; and a plurality of foilundersprings, with an underspring disposed beneath each of saidcompliant foils in each contoured lobe between adjacent retainers, thecontour of each lobe between adjacent retainers establishing aconverging wedge on the surface of said compliant foil facing saidshaft.
 14. The compliant foil fluid film radial bearing of claim 13 56wherein said generally T-shaped retainers are symmetrical.
 15. Thecompliant foil fluid film radial bearing of claim 14 16 wherein saidgenerally T-shaped asymmetrical retainers have a crosspiece with aleading edge and a trailing edge, with the leading edge thicker than thetrailing edge.
 16. The compliant foil fluid film radial bearing of claim13 56 wherein said generally T-shaped retainers are symmetricalasymmetrical.
 17. The compliant foil fluid film radial bearing of claim13 56 wherein said generally T-shaped retainers include radial openingsto provide cooling flow to said interior bore of said bushing.
 18. Thecompliant foil fluid film radial bearing of claim 13 and in additionmeans to provide cooling flow axially into said interior bore of saidbushing.
 19. A compliant foil fluid film radial bearing comprising: abushing having an interior bore including a plurality of generallyT-shaped retainers axially extending in said interior bore; a pluralityof compliant foils, with an individual compliant foil disposed in saidinterior bore of said bushing between adjacent generally T-shapedretainers; and a plurality of foil undersprings, with an underspringdisposed beneath each of said compliant foils between adjacent generallyT-shaped retainers.
 20. The compliant foil fluid film radial bearing ofclaim 19 wherein said interior bore is cylindrical and said individualcompliant foils and said individual foil undersprings beneath saidindividual compliant foils establish a converging wedge between adjacentgenerally T-shaped retainers.
 21. The compliant foil fluid film radialbearing of claim 19 wherein said interior bore is non-cylindrical,generally contoured lobes are formed between adjacent generally T-shapedretainers, and said individual compliant foils and said individual foilundersprings generally conform to the shape of said contoured lobes toestablish a converging wedge.
 22. The compliant foil fluid film radialbearing of claim 19 wherein said bearing is hydrodynamic.
 23. Thecompliant foil fluid film radial bearing of claim 19 wherein saidbearing is hydrostatic.
 24. The compliant foil fluid film radial bearingof claim 19 wherein said generally T-shaped retainers include radialopenings to provide cooling flow to said interior bore of said bushing.25. The compliant foil fluid film radial bearing of claim 19 furthercomprising: means to provide cooling flow axially into said interiorbore of said bushing.
 26. The compliant foil fluid film radial bearingof claim 13 wherein said retainers are generally T-shaped retainers. 27.A compliant foil fluid film radial bearing comprising: a bushing havinga cylindrical interior bore including a plurality of retainers axiallyextending into said interior bore; a plurality of compliant foils, withan individual compliant foil disposed in said interior bore of saidbushing between adjacent retainers; and a plurality of foilundersprings, with an underspring disposed beneath each of saidcompliant foils between adjacent retainers, the radial height of saidfoil undersprings increasing from its leading edge to its trailing edgeto establish a converging wedge of said compliant foil.
 28. Thecompliant foil fluid film radial bearing of claim 27 wherein saidretainers are generally T-shaped.
 29. The compliant foil fluid filmradial bearing of claim 28 wherein said generally T-shaped retainers areasymmetrical.
 30. The compliant foil fluid film radial bearing of claim29 wherein said generally T-shaped asymmetrical retainers have acrosspiece with a leading edge and a trailing edge, with the leadingedge thicker than the trailing edge.
 31. The compliant foil fluid filmradial bearing of claim 28 wherein said generally T-shaped retainers aresymmetrical.
 32. The compliant foil fluid film radial bearing of claim28 wherein said generally T-shaped retainers include radial openings toprovide cooling flow to said interior bore of said bushing.
 33. Thecompliant foil fluid film radial bearing of claim 27 wherein the radialstiffness of said foil undersprings increases from its leading edge toits trailing edge.
 34. The compliant foil fluid film radial bearing ofclaim 33 wherein said bearing is hydrodynamic.
 35. The compliant foilfluid film radial bearing of claim 33 wherein said bearing ishydrostatic.
 36. The compliant foil fluid film radial bearing of claim27 further comprising: means to provide cooling flow axially into saidinterior bore of said bushing.
 37. A compliant foil fluid radial bearingcomprising: a bushing having a non-cylindrical interior bore including aplurality of retainers axially extending into said interior bore; aplurality of compliant foils, with an individual compliant foil disposedin said interior bore of said bushing between adjacent retainers; and aplurality of foil undersprings, with an underspring disposed beneatheach of said compliant foils between adjacent retainers, the contour ofthe interior bore between adjacent retainers establishing a convergingwedge on the surface of said compliant foil.
 38. The compliant foilfluid radial bearing of claim 37 wherein said retainers are generallyT-shaped.
 39. The compliant foil fluid film radial bearing of claim 38wherein said generally T-shaped retainers are asymmetrical.
 40. Thecompliant foil fluid film radial bearing of claim 39 wherein saidgenerally T-shaped asymmetrical retainers have a crosspiece with aleading edge and a trailing edge, with the leading edge thicker than thetrailing edge.
 41. The compliant foil fluid film radial bearing of claim38 wherein said generally T-shaped retainers are symmetrical.
 42. Thecompliant foil fluid film radial bearing of claim 38 wherein saidbearing is hydrostatic.
 43. The compliant foil fluid film radial bearingof claim 38 wherein said generally T-shaped retainers include radialopenings to provide cooling flow to said interior bore of said bushing.44. The compliant foil fluid film radial bearing of claim 38 whereinsaid bearing is hydrodynamic.
 45. The compliant foil fluid film radialbearing of claim 37 further comprising: means to provide cooling flowaxially into said interior bore of said bushing.
 46. A radial bearingbushing comprising: a bushing having an interior bore; one or moreretainer bases axially extending into the interior bore; one or moreleading edges attached to each of the one or more retainer bases forretaining a compliant foil; and one or more trailing edges attached toeach of the one or more retainer bases for retaining a compliant foil.47. The radial bearing of claim 46 wherein the interior bore iscylindrical.
 48. The radial bearing of claim 46 wherein the interiorbore is non-cylindrical.
 49. The radial bearing of claim 46 wherein oneor more of the one or more retainer bases include radial openings toprovide cooling flow to said interior bore of said bushing.
 50. Acompliant foil radial bearing comprising: a bushing having an interiorbore including one or more retainer bases axially extending into theinterior bore; one or more compliant foils; one or more leading edgesattached to each of the one or more retainer bases for retaining acompliant foil trailing edge; one or more tailing edges attached to eachof the one or more retainer bases for retaining a compliant foil leadingedge; and one or more foil undersprings, each underspring disposedbeneath a compliant foil.
 51. The compliant foil radial bearing of claim50 wherein the interior bore in non-cylindrical, generally contouredlobes are formed between adjacent retainer bases, and an individualcompliant foil and underspring beneath the individual compliant foilgenerally conform to the shape of a contoured lobe to establish aconverging wedge.
 52. The compliant foil radial bearing of claim 50wherein said bearing is hydrodynamic.
 53. The compliant foil radialbearing of claim 50 wherein said bearing is hydrostatic.
 54. Thecompliant foil radial bearing of claim 50 wherein the one or moreretainer bases include radial openings to provide cooling flow to theinterior bore of said bushing.
 55. The compliant foil radial bearing ofclaim 50 further comprising: means to provide cooling flow axially intothe interior bore of the bushing.
 56. The compliant foil radial bearingof claim 50 wherein the interior bore is cylindrical and an individualcompliant foil and underspring beneath the individual compliant foilform a converging wedge.